This invention relates to an apparatus for detecting an in-focused condition of optical systems such, for example, as a camera and microscope or the like.
Various detecting apparatuses have heretofore been proposed which utilize two values of indices of performance each derived from the number of differences between illumination signals obtained per picture element. One of these conventional apparatuses comprises a first photosensitive element composed of a cadmium sulfide arranged in front of a focal plane of an optical system, a second photosensitive element arranged in the rear of the focal plane, a first analog-to-digital converter connected to the first photosensitive element, a second analog-to-digital converter connected to the second photosensitive element in order to obtain two digital values of indices of performance. In such apparatus, images are formed sequentially on each unit of photosensitive element by deflecting a mirror, so that the apparatus is large in size and requires complicate control operations.
In other conventional apparatus for detecting an in-focused condition of optical systems, two outputs delivered from photosensitive elements are compared with each other and during which the optical system is moved to and fro. As a result, it is difficult to precisely detect an in-focused condition. In addition, this apparatus can only detect a direction of deflection from an in-focused condition, but could not quantitatively detect its magnitude, so that the apparatus is troublesome in control and less responsive.